1. Field of the Invention
The present invention relates to a flexible tube that constitutes an insert part of an endoscope designed to be inserted into a hollow organ of the body or the like and also pertains to a method of and apparatus for producing the flexible tube More particularly, the present invention relates to a flexible tube of an endoscope which is designed so that a channel such as a biopsy, suction, air or water channel can be disposed along the outside of the flexible tube, and also pertains to a method of and apparatus for producing the flexible tube.
2. Description of the Related Art
The flexible tube of a typical conventional endoscope has heretofore been formed in the shape of an elongated tube having a circular cross-sectional configuration in such a manner that the outside of a spiral tube formed from a thin-walled, high-hardness stainless steel or phosphor bronze ribbon is covered with a braided-wire tube and the outside of the braided-wire tube is further covered with a flexible skin of a synthetic resin material.
In general endoscopes, channel tubes for biopsy and other channels are located inside the flexible tube. However, when it is desired to add second and third biopsy channels, an added biopsy channel must be located along the outside of the flexible tube. Further, there are cases where the channel tube is disposable in order to prevent transmission of bacteria and viruses from one patient to another through the endoscope. In such cases, the channel tube is located along the outside of the flexible tube.
However, since the flexible tube of the conventional endoscope has a simple circular cross-sectional configuration, if a channel tube is located along the outside of the flexible tube, the channel tube protrudes from the flexible tube and this prevents the flexible tube from being smoothly inserted into the patient's body and can inflict extra pain on the patient.
To overcome this problem, a U-shaped groove may be formed in the outer peripheral surface of the flexible tube along the axis thereof to receive a channel tube in the groove on the outer side thereof.
However, the flexible tubes of endoscopes need to be sufficiently strong to bear bending and crushing loads and, at the same time, must have high flexibility so that these tubes bend smoothly along the inner wall of a hollow organ of the patient's body. To meet the requirements, it is essential to employ a spiral tube made of a thin-walled, high-hardness material. However, it is not easy to form a U-shaped groove in a high-hardness material. If a U-shaped groove is axially formed in the outer surface of a spiral tube, the tube is likely to be twisted due to the residual strain or the like and it is therefore very difficult to form a U-shaped groove in a straight-line form.
It may be considered that the following press forming process is the best method of forming a U-shaped axial groove in the outer peripheral surface of a spiral tube, that is, a core bar which is formed with a groove (female die) having the same configuration as that of the desired U-shaped groove is inserted into a spiral tube and, in this state, the tube is pressed from the outer side thereof along the U-shaped groove in the core bar. In actual practice, however, such press forming process causes the spiral tube and the core bar to adhere to each other so strongly that the core bar cannot be removed from the spiral tube. Therefore, it is impossible with this method to produce a spiral tube having a U-shaped groove extending along the axis of the tube.
If the spiral tube is twisted, a kink is generated at every turn of the spiral, which causes the problem that an optical fiber bundle or the like is caught and damaged by such a kink. Due to these problems, it has heretofore been difficult to form a U-shaped groove for receiving a channel tube in the outer peripheral surface of a flexible tube in a straight line along the axis of the tube.